Many electronic devices are used to transfer or store sensitive information. For example, a card reader may read, process, and at least temporarily store data related to credit cards, bank accounts and pin numbers and transfer data to a computer for the purpose of conducting a transaction. These devices may be subjected to tampering.
A cover may prevent tampering and/or provide evidence that a tampering has been tempted. One such device, disclosed in German Patent DE4312905, provides a flexible substrate that has a number of conductors forming one or more electrical circuits, disposed between a key pad and a PCB. The conductors have a narrow width and are finely spaced and spread over the substrate so as to form a barrier against forming a hole in the substrate without severing a conductor. The conductors are connected to an alarm circuit which is triggered by a conductor being severed. The response to the triggering of the alarm depends on the arrangement of the alarm circuit and may range from simply raising an alarm indication to disabling the protected circuit, or completely erasing data stored in the device. Key switches are arranged to be operated by depressing keys of the key pad which cause momentary deformation of the security device to allow conductive portions formed on the security device to short across or electrically interconnect selected conductive tracks of the PCB. Alarm switches are provided which function in a similar manner to the key switches and are held in the closed position by spigots formed on a housing containing the PCB to raise an alarm condition when the housing is opened.
A similar design is disclosed in US published patent application no. U.S. 2011/0100788A1, in which the protection device is connected to the circuit board via two normally open switch contacts. This design requires the protected circuit to be at all times enclosed by a secondary housing that applies a force against the protection device to resiliently deform a part of a substrate of the protection device to continually maintain the switches in the closed condition, so that the alarm circuit will be immediately triggered by opening of the housing. In this design the alarm switches are used to electrically connect the conductor(s) of the protection device to the security terminals of the PCB. Opening the housing would open the switch and trigger the security alarm. However, as there is only one type of alarm trigger, even if there is more than one trip switch, there is no indication of what caused the alarm to trigger, e.g., opening of the housing or damage to the conductor.
Hence there is a desire for a simplified device for protecting an electronic circuit incorporating a keyboard.